The objective of the proposed research is to understand physiological mechanisms underlying auditory-vocal interaction in primates. Currently such mechanisms are poorly understood, and there are no adequate primate models available to address these issues. In this application, we will examine our research questions in a highly vocal primate, the common marmoset (Callithrix jacchus). The marmoset provides several important advantages for our studies over other primate species: a rich vocal repertoire and a high reproductive rate while in captivity. In the proposed research, we will examine two fundamental questions concerning auditory-vocal interaction in primates: 1) Does the vocal production system influence cortical processing of auditory information? 2) Is auditory input necessary to maintain normal vocal production? Specifically, we will test the hypothesis that the vocal production system modulates neural responses in the auditory cortex in primates. Furthermore, we will determine spatial distributions of neurons exhibiting vocalization-related modulated in the auditory cortex. Our preliminary data indicates that neural responses in the auditory cortex are modulated by the vocal production system, with the modulation starting prior to the vocal onset. In the second series of experiments, we will study developmental changes in marmoset vocalizations and its dependence on the auditory experience. Our hypothesis is that marmoset vocalizations undergo postnatal changes under the normal auditory environment. We will further test the hypothesis that auditory feedback is necessary for maintaining normal vocal productions. The proposed research will approach the issues related to auditory-vocal interaction in an integrated manner. Aims 1-2 and 3-4 represent intellectually linked efforts to study auditory-vocal interaction from two directions: Aims 1-2 investigate modulation of auditory processing by the vocal system, whereas Aims 3-4 investigate modulation of vocal production by the auditory system. Findings of this research will provide insight into speech production and perception mechanisms in humans and establish a parallel non-haman primate model to investigate disease-related issues in speech and hearing.